Electric machines such as motors and generators are widely employed in industrial and commercial facilities. These machines are relied upon to operate with minimal attention and provide for long, reliable operation. Many facilities operate several hundreds or even thousands of such machines concurrently, many of which are integrated into a large interdependent process or system. Like most machinery, at least a small percentage of such induction motors are prone to failure. The majority of such failures can be attributed to either mechanical failures and/or thermal failures of the motor insulation.
Other than normal aging, failures are typically due to: poor or no maintenance; improper application (e.g., wrong enclosure, excessive loading, etc.); and improper installation (e.g., misalignment, bad power, inverter mismatch, etc.). Even with normal aging failures, it is desirable to provide low cost failure prediction information for such machines.
Depending on the application, the failure of a machine in service can possibly lead to system or process down time, inconvenience, and possibly, even a hazardous situation. Thus, it desirable to diagnose the machinery for possible failure or faults early in order to avoid such problems. Absent special monitoring for certain motor problems, the problems may have an insidious effect in that although only a minor problem on the onset the problem could become serious if not detected. For example, insulation problems and electrical problems may not become apparent until irreversible damage has resulted. Likewise, bearing problems due to inadequate lubrication, contamination or other causes may not become apparent until irreversible damage has occurred.
Vibration analysis is the established technique for determining the health of mechanical components in rotating machinery such as induction motors. To obtain vibration data for machinery analysis, accelerometers as well as associated sampling and filtering techniques are often employed. Larger machines and/or systems may employ proximity detectors to determine vibration.
In using accelerometers, the accelerometers are mounted on the machine being monitored, which also requires access to the machine to mount the sensors during testing. The location and orientation of the accelerometers are critical to the characteristics of the signal obtained. A vibration generated in one part of the machine is transmitted through the solids separating the source from the accelerometer. The analysis of the vibration signals taken at various times is dependent on the ability to reproduce the precise location and direction of mounting of the accelerometers. Thus, in most cases, accelerometers and/or their mounting fixtures are permanently installed on the equipment to be monitored.
Since accelerometers sense vibration primarily in one direction, multiple sensors are typically necessary to detect the vibrations generated in other directions and in different parts of some equipment. Thus, in order to sense all significant vibration directions, it may be necessary to install multiple-axis sensors. The results obtained are then combined and analyzed to develop the diagnostic information. To obtain good vibration data in order to perform the analysis it is desired to cover 5 axes with accelerometers (e.g., a 3-axis accelerometer at the load-end of the machine and a 2-axis accelerometer at the other end). However, these accelerometers are generally very expensive, the cost of which may exceed the price of the machine being analyzed.
There are alternative techniques (e.g., current signature analysis) other than vibration analysis for analyzing a machine. However, mechanical problems of a machine usually are manifested most prominently via vibrations. Thus vibration analysis is still the desired method for analyzing a machine for mechanically related problems. Furthermore, since so much of machine analysis and diagnosis has been done through vibration analysis, there is an extensive amount of historical vibration signature data available for use in determining the health of a machine.
Consequently, there is a strong need in the art for a method and/or system for analyzing a machine for mechanical problems using classical vibration analysis technique without having to employ expensive vibration sensors to carry out the analysis.